The present invention relates generally to power tools, and more particularly provides an improved hydraulic power wrench for tightening and loosening threaded fasteners such as nuts or bolts.
As exemplified in U.S. Pat. Nos. 4,201,099; 4,336,727; 4,423,649; 4,233,865; 4,368,655; and 4,513,644, a variety of hydraulically powered wrench designs have been previously proposed for the transmission of rotational power to threaded fasteners. A common constructional theme has been to provide a hydraulically driven piston within the wrench housing and to utilize the translational piston motion to rotationally drive an output shaft carried by the housing and connectable to a threaded fastener to be tightened or loosened. This linear-to-rotational motion conversion is typically accomplished by positioning a drive element, such as a pin member, between the piston and the shaft, and interconnecting the drive member between the piston and output shaft with suitable pivotal linkage members.
A drive ratchet locked to the output shaft within the housing is rotationally driven in a first direction, by a pawl carried by the linkage members between the drive member and shaft, during the forward power stroke of the piston and drive member. During the rearward return stroke of the piston and drive member, reverse rotation of the output shaft is precluded by a second ratchet and pawl mechanism disposed within the wrench housing.
As the threaded fastener is being tightened by the wrench, it is a common practice to brace a portion of the housing against a suitable adjacent support surface to prevent undesirable reactive rotation of the housing about the output shaft. This bracing technique is often facilitated by the provision of a reaction brace plate or arm member secured to the housing in a spaced relation with the output shaft and adapted to engage the adjacent support surface.
In theory at least, power wrenches of this general design are well suited to provide a predetermined amount of torque to threaded fasteners in a variety of applications requiring a heavy duty tool able to withstand often harsh environments, rough handling and high internal and external forces. In practice, however, such wrenches have proven to be subject to premature mechanical failure as well as having various operational limitations associated therewith.
A key mechanical failure point in such wrenches has been in the linkage region between the piston and the internal drive pin. Conventional interconnecting means used in this critical area have simply not been of sufficient strength, durability and ruggedness to suitably withstand the large hydraulic forces transmitted to the drive pin via the piston during its power stroke. Such linkage has been subject to premature failure or breakage and/or has been prone to cause premature and excessive wearing of the drive pin.
Another limitation commonly associated with hydraulic power wrenches of this type is related to their inaccessably disposed internal anti-reverse pawl and ratchet mechanism which prevents reverse rotation of the output shaft during the return stroke of the piston. If the maximum wind-up force on the fastener being tightened occurs while the piston is at some intermediate position of its power stroke, this mechanism can lock the entire drive mechanism of the wrench with the wrench housing being very tightly braced against its adjacent support surface. This can make it very difficult to remove the wrench from the fastener and the support surface, and can cause undesirable equipment downtime.
The bracing structures conventionally used in power wrenches of this type give rise to yet another operational limitation in that they are either fixed in a single position to the wrench housing or are positionally adjustable relative to the housing only to a very limited degree. This, of course, limits the usefulness of the bracing structure where adjacent support surfaces are not suitably positioned to be engaged by such structure.
It can be seen from the foregoing that a need exists for an improved hydraulic power wrench which eliminates or minimizes the above-mentioned and other limitations and disadvantages commonly associated with power wrenches of conventional design. It is accordingly an object of the present invention to provide such a wrench.